Updated 7/01/2011 at 8:00 p.m.

CHICAGO (CBS)– Hailstones the size of large marbles rained down on the Garfield Park Conservatory Thursday night, smashing tens of thousands of window panes that cover three of the giant greenhouses and causing widespread damage to the plants.  

This historic site — it is closed indefinitely – suffered damage that some say will go into the millions of dollars. The hail shattered 50 percent of the glass panes at the conservatory, and dangerous shards hung precariously overhead on Friday, threatening to crash down.

Mary Eysenbach, the director of conservatories,  agreed the repair project will be enormous.

“The Garfield Park Conservatory is 2 acres under glass — that’s just the display houses,” she told CBS 2.

Chicago Park District officials are particularly worried about the Fern Room, which was designed by celebrated architect Jens Jensen and is more than 100 years old.

“There are thousands of plants in there,” Eysenbach said. “Some of those plans are original to the Jens Jensen construction.”

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The longtime head of the Garfield Conservatory Alliance, a volunteer group, was devastated.

“It does tear at my heart,” Eunita Rushing said. “All I could think of was, this is my baby. I looked at that fern room where we have that significant, historic collection in there, and it just ripped my heart out.”

Alliance board member Patrick Deady says repair estimates are $4 million to $5 million, and that may go higher.

The organization has already begun soliciting financial donations to help repair Garfield Park Conservatory. Click here to learn more.

Some good news emerged Friday. Two weddings over the holiday weekend would be allowed to go on as scheduled. The area that will host the functions is intact.

“We’re very lucky and very thankful for that,” event coordinator Joan Colon said.

The historic glass building, at 300 N. Central Park Ave., is typically open every day of the year. It includes several indoor gardens, showcasing a variety of plants. It is one of the largest conservatories in the country.

The cost of damage has not been determined, and it could be several days before the West Side landmark can open again.

There have been no reports of damage at the Lincoln Park Conservatory, which has similar construction.